Magnetic tape cartridge

ABSTRACT

Disclosed herein is a magnetic tape cartridge including a reel-rotation restraining member which restricts rotation of a reel when not used and allows the rotation of the reel when used. The reel-rotation restraining member has a restraining member, an urging member, and an unlocking member. The restraining member has a restraining gear which meshes with a locking tooth portion, and the restraining member is supported by a support portion of the cartridge case. In the magnetic tape cartridge, the following relationship is met: 
     
       
           b≦ (2× a×c )/ d   
       
     
     where “a” represents the length of engagement between the restraining member in an unlocked state and the support portion, “b” represents the clearance between the restraining member and the support portion, “c” represents the space between the tooth of the restraining gear and the locking tooth portion, and “d” represents the outside diameter of the restraining gear.

This is a divisional of application Ser. No. 09/825,943 filed Apr. 5,2001 now U.S. Pat. No. 6,499,686; the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic tape cartridge and moreparticularly relates, in a magnetic tape cartridge where a single reelwith magnetic tape wound thereon is rotatably housed within a cartridgecase, to the structure of reel-rotation restraining means which causesthe reel to be in a rotation-restrained state when not being used.

2. Description of the Related Art

In the magnetic tape cartridges, which are used as storage medium to beemployed in external storage units for computers, etc., there is known atype where a single tape reel with magnetic tape wound thereon isrotatably housed within a cartridge case. This magnetic tape is employedas a data archiving tape for computers, etc., and stores importantinformation. For this reason, the magnetic tape cartridge is providedwith reel-rotation restraining means for restricting rotation of thereel so that problems, such as tape jamming, etc., do not occur and thatthe magnetic tape is not pulled out from the cartridge case unexpectedlywhen not being used, such as when being archived, etc.

The reel-rotation restraining means, as disclosed in Japanese UnexaminedPatent Publication No. 11 (1999)-23835, is equipped with a restrainingmember for restricting rotation of the reel, an urging member for urgingthe restraining member in a restraining direction, and an unlockingmember for moving the restraining member in an unlocking direction inaccordance with the chucking operation of the rotation means of thedrive mechanism of a drive unit such as a recording-reproducing unit.

A locking tooth portion is formed on the reel side, while a restraininggear meshable with the locking tooth portion is provided on the side ofthe restraining member provided so that it cannot rotate with respect tothe cartridge case. In the non-operative state, the restraining gear ofthe restraining member engages the locking tooth portion of the reel torestrict unexpected rotation of the reel, whereby the magnetic tapewound on the reel can be locked. On the other hand, if the magnetic tapecartridge is loaded into the drive unit, the unlocking member moves therestraining member to disengage the restraining gear of the restrainingmember from the locking tooth portion of the reel. In the disengaged orunlocked state, the reel is rotatable and therefore the magnetic tapecan be loaded into or unloaded from the drive unit.

The above-mentioned unlocking member is equipped with a main body whichabuts the above-mentioned restraining member, and leg portions whichabut the rotation means of the drive mechanism of the drive unit. Whenthe chucking operation of the rotation means is performed, the rotationmeans moves the unlocking member upward to disengage the retraining gearof the restraining member from the locking tooth portion of the reel.

In the case where a magnetic tape cartridge is equipped with thereel-rotation restraining means mentioned above, incidentally, therestraining member in the unlocked state is unstable because the centralportion of the restraining member is supported only by the centralportion of the unlocking member. On the other hand, because the reel isrotated or stopped according to loading or unloading of the magnetictape, the force exerted on the reel is transmitted to the restrainingmember through the unlocking member. For this reason, the restrainingmember tends to tilt. If the restraining member tilts, the restraininggear thereof will contact the locking tooth portion of the reel. Thisproduces an undesirable sound, disturbs rotation of the reel, andinterferes with the operation of loading or unloading magnetic tape.

In addition, in the case where the magnetic tape slackens because of theshock produced by the magnetic tape cartridge falling when not beingused, the magnetic tape cartridge cannot absorb the slack of themagnetic tape because it has only a single reel within the cartridgecase. As a result, there is a fear that the magnetic tape will bedamaged. Hence, in order to prevent the magnetic tape from slackeningbecause of shock caused by the cartridge falling, the locking toothportion of the reel and the restraining gear are constructed so that thetooth face of the locking tooth portion, which faces in the reversewinding direction (tape slackening direction), and the tooth face of therestraining gear, which abuts the tooth face of the locking toothportion, are inclined at an angle near to 90 degrees.

However, in the case where the reel in the non-operative state isunexpectedly locked by the mesh between the restraining gear and thelocking tooth portion, there are cases where the reel is freely moved bythe complete mesh between the restraining gear and the locking toothportion, depending on the phase relationship between the two in theunmeshed state. Particularly, if the tooth face of the locking toothportion, which faces in the reverse winding direction (tape slackeningdirection), and the tooth face of the restraining gear, which abuts thetooth face of the locking tooth portion, are inclined at an angle nearto 90 degrees in order to prevent slackness, as described above, thelocking tooth portion and the restraining gear move only in the windingdirection when they mesh with each other, and consequently, force isexerted on the magnetic tape in the winding direction.

In addition, in the case of a magnetic tape cartridge with magnetic tapewound on a single reel, a tape leader member is coupled with the leadingend of the magnetic tape, and the tape leader member is caught by thecatching member of the drive mechanism of a drive unit to pull out themagnetic tape from the cartridge case. In this construction, if the tapeleader member is exposed to the case peripheral side, there is a problemthat the free end will project from the cartridge case, or dust willenter the cartridge case through a tape leader opening formed in thecartridge case, when the magnetic tape cartridge is subjected to afalling shock, etc. Hence, it is disclosed in Japanese Unexamined PatentPublication No. 11 (1999)-232828 that a tape leader pin is retainedinside a tape leader opening which is closed or opened by a slide door.The configuration of the tape leader member is determined mainly byspecifications for the recording-reproducing unit.

Thus, in the case where the tape leader pin is coupled with the leadingend of the magnetic tape, and the tape leader pin is retained within thecartridge case during the non-operative state, if the reel is moved inthe winding direction and a pulling force greater than a predeterminedquantity is exerted on the magnetic tape, there is a fear that themagnetic tape and the tape leader pin will be easily disengaged fromeach other, because the strength of the engagement of the tape leaderpin with the magnetic tape is relatively low. Even when the two are notdisengaged, the magnetic tape will be stretched by the aforementionedpulling force. Because of this, the magnetic recording-reproducingcharacteristics are degraded, or the tape leader pin is shifted out of apredetermined retaining position or tilted. Thereafter, there is a fearthat the magnetic tape cannot be correctly loaded into the drive unitand therefore reliability will be reduced.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedpoints. Accordingly, it is a first important object of the presentinvention to provide a magnetic tape cartridge which is capable ofpreventing the contact between a restraining gear and a lockingprotrusion that is caused by the tilt of the restraining member.

A second important object of the invention is to provide a magnetic tapecartridge that is capable of preventing the disengagement of themagnetic tape from a tape leader pin which is caused by the magnetictape pulled in the locked state when subjected to a falling shock, whileassuring the locked state of a reel obtained in a non-operative by therestraining member of reel-rotation restraining means.

To achieve the first object of the present invention and in accordancewith the present invention, there is provided a first magnetic tapecartridge comprising:

a cartridge case where a single reel with magnetic tape wound thereon isrotatably housed; and

reel-rotation restraining means which, when not used, goes to a lockedstate to restrict rotation of the reel and, when used, goes from thelocked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

wherein the restraining member has a restraining gear which meshes witha locking tooth portion formed in the reel to restrain rotation of thereel, the restraining member being supported by a support portion of thecartridge case so that it is slidable without being rotated; and

the following relationship is met:

b≦(2×a×c)/d

where “a” represents the length of engagement between the restrainingmember in the unlocked state and the support portion, “b” represents theclearance between the restraining member and the support portion, “c”represents the space between a tooth of the restraining gear and thelocking tooth portion, and “d” represents the outside diameter of therestraining gear.

In accordance with the present invention, there is provided a secondmagnetic tape cartridge comprising:

a cartridge case where a single reel with magnetic tape wound thereon isrotatably housed; and

reel-rotation restraining means which, when not used, goes to a lockedstate to restrict rotation of the reel and, when used, goes from thelocked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

wherein the reel has a reel gear which meshes with a driving gear ofdrive means of the drive unit;

the unlocking member has a main body which abuts the restraining member,and leg portions whose lower ends abut part of the drive means of thedrive unit through guide holes provided to penetrate the reel gear; and

in the locked state, the lower ends of the leg portions of the unlockingmember project from a tooth edge of the reel gear.

In accordance with the present invention, there is provided a thirdmagnetic tape cartridge comprising:

a cartridge case where a single reel with magnetic tape wound thereon isrotatably housed; and

reel-rotation restraining means which, when not used, goes to a lockedstate to restrict rotation of the reel and, when used, goes from thelocked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

wherein the restraining member has a restraining gear which meshes witha locking tooth portion formed in the reel to restrain rotation of thereel, the restraining member being supported by a support portion of thecartridge case so that it is slidable without being rotated; and

in the unlocked state, the space between a tooth of the restraining gearand the locking tooth portion is set to a length greater than or equalto a tooth depth of the restraining gear.

In the third magnetic tape cartridge, it is preferable that theaforementioned space be set greater than or equal to 1.2 times the toothdepth of the restraining gear. It is further preferable that theaforementioned space be set greater than or equal to 1.4 times the toothdepth of the restraining gear.

In accordance with the present invention, there is provided a fourthcartridge case where a single reel with magnetic tape wound thereon isrotatably housed; and

reel-rotation restraining means which, when not used, goes to a lockedstate to restrict rotation of the reel and, when used, goes from thelocked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

wherein either a slide portion of the restraining member or a slideportion of the unlocking member is formed into a curved surface whichhas a radius of curvature of 30 mm or less.

In the fourth magnetic tape cartridge, it is preferable that the radiusof curvature of the curved surface be 20 mm or less. It is furtherpreferable that the radius of curvature of the curved surface be 15 mmor less.

In accordance with the present invention, there is provided a fifthmagnetic tape cartridge comprising:

a cartridge case where a single reel with magnetic tape wound thereon isrotatably housed; and

reel-rotation restraining means which, when not used, goes to a lockedstate to restrict rotation of the reel and, when used, goes from thelocked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

wherein the restraining member has a restraining gear which meshes witha locking tooth portion formed in the reel to restrain rotation of thereel;

the urging member is supported by a spring receiver formed in thecartridge case; and

the following relationship is met:

e≦(2×f×c)/d

where “c” represents the space between a tooth of the restraining gearin the unlocked state and the locking tooth portion, “d” represents theoutside diameter of the restraining gear, “e” represents the clearancebetween an outer periphery of the urging member and an inner peripheryof the spring receiver, and “f” represents the length of engagementbetween the urging member and the spring receiver.

To achieve the aforementioned second object of the present invention andin accordance with the present invention, there is provided a sixthmagnetic tape cartridge comprising:

a cartridge case where a single reel with magnetic tape wound thereon isrotatably housed; and

reel-rotation restraining means which, when not used, goes to a lockedstate to restrict rotation of the reel and, when used, goes from thelocked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

wherein the restraining member has a restraining gear which meshes witha locking tooth portion formed in the reel to restrain rotation of thereel; and

a tooth of the restraining gear has two inclined faces which have anapex angle and interior angles, the apex angle being between an apexangle of the locking tooth portion of the reel and 90 degrees, and theinterior angles being 30 degrees or greater with respect to a verticalline and also being approximately the same.

Note that the aforementioned vertical line refers to a line vertical tothe direction of rotation of the reel. Also, in the sixth magnetic tapecartridge, it is preferable that the locking tooth portion and the toothof the restraining gear be formed from synthetic resin material.

The present invention has the following advantages:

(1) In the reel-rotation restraining means, which has a restrainingmember for restricting rotation of the reel by moving toward or awayfrom the reel, an urging member for urging the restraining member in arestraining direction, and an unlocking member for moving therestraining member in an unlocking direction, by rotating integrallywith the reel and moving according to a chucking operation of rotationmeans of a drive unit,

the following relationship is met:

 b≦(2×a×c)/d

where “a” represents the length of engagement between the restrainingmember in the unlocked state and the support portion, “b” represents theclearance between the restraining member and the support portion, “c”represents the space between a tooth of the restraining gear and thelocking tooth portion, and “d” represents the outside diameter of therestraining gear; or the following relationship is met:

e≦(2×f×c)/d

where “c” represents the space between a tooth of the restraining gearin the unlocked state and the locking tooth portion, “d” represents theoutside diameter of the restraining gear, “e” represents the clearancebetween an outer periphery of the urging member and an inner peripheryof the spring receiver, and “f” represents the length of engagementbetween the urging member and the spring receiver. With thisarrangement, tilting of the restraining member is suppressed in theunlocked state. Therefore, the contact between the restraining gear andthe locking tooth portion can be prevented and the major causes of anundesirable sound and a hindrance to the rotation of the reel can beeliminated.

(2) In the locked state, the lower ends of the leg portions of theunlocking member project from the tooth edge of the reel gear. Also, inthe unlocked state, the space between the tooth of the restraining gearand the locking tooth portion is set to a length greater than or equalto the tooth depth of the restraining gear. With this arrangement, theextent of movement of the restraining member in the unlocked stateincreases. Therefore, even if the restraining member tilts slightly, thecontact between the restraining gear and the locking tooth portion canbe prevented and the major causes of an undesirable sound and ahindrance to the rotation of the reel can be eliminated.

(3) Either a slide portion of the restraining member or a slide portionof the unlocking member is formed into a curved surface which has aradius of curvature of 30 mm or less. With this, when the restrainingmember tilts, restoring force to a flat state that equalizes the urgingforce produced by the urging member in the circumferential direction isenhanced and tilting of the restraining member is suppressed. Therefore,the contact between the restraining gear and the locking protrusion canbe prevented and the major causes of an undesirable sound and ahindrance to the rotation of the reel can be eliminated.

(4) The tooth of the restraining gear has two inclined faces which havean apex angle and interior angles, the apex angle being between an apexangle of the locking tooth portion of the reel and 90 degrees, and theinterior angles being 30 degrees or greater with respect to a verticalline and also being approximately the same. That is, the interior anglesare within 45 degrees. With this, in the meshed state between therestraining gear and the locking tooth portion, the reel can be reliablylocked. Even if the two are shifted in phase when locked and thereforethe reel is moved in the reverse winding direction, the extent ofmovement will be slight and therefore the slack of the magnetic tapewill also be slight. Also, even if the reel is moved in the windingdirection because of the mesh between the two, the extent of movementwill be slight and therefore a pulling force that is exerted on themagnetic tape by the movement of the reel 2 will be small. Therefore,the disengagement of the magnetic tape from the tape leader pin due toforced locking can be prevented.

(5) When the reel is rotated in the winding direction by falling shock,etc., and an excessive pulling force is exerted on the magnetic tape,the restraining member is moved in the unlocking direction by theinclined face of the locking tooth portion which faces in the reversewinding direction. As a result, the meshed state between the restrainingmember and the locking tooth portion becomes shallow and the rotation ofthe reel in the reverse winding direction is allowed. Therefore, anexcessive pulling force can be alleviated and the disengagement of themagnetic tape from the tape leader pin can be prevented.

(6) The apex angle of the tooth of the restraining gear of therestraining member is set to an angle greater than the apex angle of thelocking tooth portion of the reel. That is, the tooth edge of thelocking tooth portion of the reel is made thinner by setting the apexangle of the locking tooth portion to an angle less than the apex angleof the tooth of the restraining gear of the restraining member. As aresult, the locking tooth portion becomes easy to deform, and slightplay can be provided between the teeth. Therefore, a force to pull themagnetic tape can be alleviated without reducing the forced lockingfunction. Particularly, in the case where the restraining gear and thelocking tooth portion are formed from synthetic resin material, thefunction of alleviating the pulling force to be exerted on the magneticforce is enhanced because they are easily deformable.

(7) Thus, according to the present invention, reliable locking of thereel in the non-operative state, and alleviation of a magnetic-tapepulling force that is produced in the locked state by falling shock,etc., are compatible with each other. This can enhance reliability,while preventing stretching and disengagement of the magnetic tape andassuring magnetic recording-reproducing characteristics and a correctoperation of loading the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in further detail with referenceto the accompanying drawings wherein:

FIG. 1 is a front sectional view of a magnetic tape cartridge of anembodiment of the present invention in the non-operative state;

FIG. 2 is a part-sectional view of the essential parts of the magnetictape cartridge of FIG. 1 in the operative state;

FIG. 3 is a part-sectional view taken substantially along line A—A ofFIG. 2;

FIG. 4 is a part-sectional view showing the tilted state of therestraining member shown in FIG. 2;

FIG. 5 is a part-sectional view showing the positional relationshipsbetween parts, obtained according to a form for suppressing the tilt ofthe restraining member;

FIG. 6 is a part-sectional view showing the positional relationshipsbetween parts, obtained according to another form for suppressing thetilt of the restraining member; and

FIG. 7 is an enlarged sectional view taken substantially along line B—Bof FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a preferred embodiment of a magnetictape cartridge in accordance with the present invention. The magnetictape cartridge 1 is equipped with a cartridge case 3, which is formed byfastening an upper case 31 and a lower case 32 together with smallscrews, etc. The lower case 32 is provided at a center portion thereofwith an opening 32 a. A single reel 2 with magnetic tape (not shown)wound thereon is housed rotatably within the cartridge case 3. Themagnetic tape cartridge 1 is further equipped with reel-rotationrestraining means 10, which allows rotation of the reel 2 when beingused and restricts the rotation when not being used.

The reel 2 consists of a bottomed cylindrical reel hub 21, wheremagnetic tape is wound on the outer periphery, and upper and lowerflange portions 22 and 23 respectively projected in disk form in theradial direction from the upper and lower ends of the outer periphery ofthis reel hub 21. The reel hub 21 and the lower flange portion 22 areintegrally formed from synthetic resin and are united with the upperflange portion 23, for example, by ultrasonic welding. The reel hub 21is closed at a lower portion thereof by a bottom wall 21 a. The radiallyouter portion of the bottom surface of the bottom wall 21 a has anannular reel gear 24 that meshes with the driving gear 13 of rotationmeans 11 provided in a cartridge drive mechanism (not shown). A reelplate 25 for magnetic suction is formed from an annular metal plate andis attached inside the reel gear 24. The reel gear 24 and reel plate 25of the reel 2 are disposed to face the opening 32 a in the bottomsurface of the cartridge case 3. Note that the reel 2 is urged downwardby an urging member 5 to be described later.

On the other hand, the rotation means 11 of the cartridge drivemechanism is equipped on the upper end surface of a rotating shaft 12with the annular driving gear 13 and a driving magnet (not shown). Inthe chucking operation, the magnetic tape cartridge 1 loaded into abucket (not shown) on the driving side is lowered toward the rotatingshaft 12. Then, the driving gear 13 meshes with the reel gear 24, andthe reel plate 25 inside the reel gear 24 is attracted by the drivingmagnet provided inside the driving gear 13, whereby the meshed statebetween the driving gear 13 and the reel gear 24 is held.

Next, a description will be given of the mechanism of the reel-rotationrestraining means 10. This reel-rotation restraining means 10 isequipped with a restraining member 4 movable toward or away from thereel 2 in an up-and-down direction; an urging member 5, formed from acoil spring, for urging the restraining member 4 in a restrainingdirection; and an unlocking member 6 for moving the restraining member 4in an unlocking direction.

Three guide holes 26 penetrating the reel gear 24 in the up-and-downdirection are disposed in the bottom wall 21 a of the reel 2 at regularintervals on a circle (see FIG. 4). Furthermore, three pairs of lockingprotrusions (i.e., 6 locking protrusions) 27 are erected in the topsurface of the bottom wall 21 a at regular intervals on a circle atpositions different in phase from the guide holes 26 (see FIG. 3). Theupper end portion of each locking protrusion 27 is formed into a lockingtooth portion 29. Note that three or more guide holes 26 may bedisposed. Also, three or more pairs of locking protrusions 27 may bedisposed. Furthermore, the locking tooth portion 29 of the upper end ofthe locking protrusion 27 may be constructed of a single tooth.

The restraining member 4, formed from synthetic resin material, has adisc portion 41 within the reel hub 21 of the reel 2. The disc portion41 is disposed to face the bottom wall 21 a of the reel 2. A restraininggear 42 is formed in annular form in the radially outer portion of thebottom surface of the disc portion 41 and is meshable with the lockingtooth portion 29 of the locking protrusions 27. In addition, the centerportion of the bottom surface of the disc portion 41 is projecteddownward and formed into a slide portion 41 a. The slide portion 41 a isengageable with the slide portion 61 a of the top surface of the mainportion 61 of the unlocking member 6 to be described later by the urgingforce of the urging member 5 of the reel-rotation restraining means 10.

Furthermore, a protruding portion 44 extends upward from the top surfaceof the disc portion 41 of the restraining member 4. The protrudingportion 44 is provided with a stopper groove 45 in the form of a cross,which extends in the up-and-down direction. On the other hand, a supportportion (swivel stopping protrusion) 33 that is inserted into thestopper groove 45 is erected in the inside surface of the upper case 31of the cartridge case 3. If the stopper groove 45 and the supportportion 33 are engaged with each other, the restraining member 4 canmove in the up-and-down direction without rotating. While the supportportion 33 in this embodiment is provided inside the restraining member4, it may be provided outside the restraining member 4.

The urging member (e.g., a coil spring) 5 is interposed between the topsurface, outside the protruding portion 44, of the disc portion 41 ofthe restraining member 4 and the inside surface, outside the supportportion 33, of the upper case 3. The urging member 5 is used for urgingthe restraining member 4 downward in the locking direction where therestraining gear 42 and the locking tooth portion 29 engage with eachother.

The unlocking member 6 is interposed between the restraining member 4and the bottom wall 21 a of the reel hub 21 so that it is movable up anddown. For this reason, three cylindrical leg portions 63 extending inthe up-and-down direction are provided on the bottom surface of thetriangular main body 61 corresponding to the vertexes of the main body61. The leg portions 63 are inserted into the guide holes 26 of thebottom wall 21 of the reel 2 so that they are movable into and out ofthe guide holes 26. The lower ends of the leg portions 63 are located toface the tooth portion of the reel gear 24 of the bottom surface of thereel 2. With the leg portions 63 inserted into the guide holes 26, eachpair of locking protrusions 27 is located between two adjacent legportions 63 and outside the main body 61 of the unlocking member 6. Notethat the leg portion 63 may be formed into the shape of a square pillar,an elliptic cylinder, etc.

When the unlocking member 6 is at the lowest position (see FIG. 1), thelower ends of the leg portions 63 of the unlocking member 6 project fromthe reel gear 24. When, at the lowest position, the driving gear 13 ismeshed with the reel gear 24 by the chucking operation of the rotationmeans 11 of the cartridge drive mechanism (not shown), the unlockingmember 6 is pushed upward by a predetermined quantity of stroke (seeFIG. 2). Also, the unlocking member 6 is rotated integrally with thereel 2 by the fit of the leg portions 63 into the guide holes 26.

The reel 2 is provided with guide members 28 for guiding part of theunlocking member 6 in the direction of insertion when inserting the legportions 63 of the unlocking member 6 into the guide holes 26 (see FIG.3). Each guide member 28 is formed on the inside wall, near the guidehole 26, of the reel hub 21 of the reel 2 and is constructed of twoguide ribs, which extend in the up-and-down direction (i.e., thedirection in which the leg portions 63 are inserted), for guiding thevertex of the triangular main body 61 of the unlocking member 6. Also,similar reinforcement ribs are disposed over the inner peripheralsurface of the reel hub 21.

In the unlocked state of the reel-rotation restraining means 10,incidentally, the restraining member 4 is unstable and tends to tilt,because only the central portion of the bottom surface of therestraining member 4 is in contact with the central portion of theunlocking member 6. On the other hand, since the reel 2 is rotated orstopped when magnetic tape is loaded or unloaded, the force produced bythe loading or unloading operation is exerted on the restraining member4 through the unlocking member 6. Therefore, if the restraining member 4is tilted as shown in FIG. 4 by the produced force, the restraining gear42 of the restraining member 4 will be brought into contact with thelocking tooth portion 29 of the reel 2 and will produce an undesirablesound. Because of this, rotation of the reel 2 is disturbed and theoperation of loading or unloading magnetic tape cannot be performed withstability.

Hence, in the present invention, a structure for suppressing the tilt ofthe restraining member 4 that is in the unlocked state is adopted in thereel-rotation restraining means 10. As a first form of the tiltsuppressing structure, in a stopper structure, which is constructed ofthe stopper groove 45 of the protruding portion 44 and the supportportion 33 of the upper case 31, for supporting the restraining member 4on the upper case 31 so that it is movable in the up-and-down directionwithout rotating, as shown in FIG. 5, the following dimensionalrelationship is met:

b≦(2×a×c)/d

where “a” represents the length of engagement between the restrainingmember 4 and the support portion 33 of the upper case 31, “b” representsthe clearance between the restraining member 4 and the support portion33, “c” represents the space between the restraining gear 42 and thelocking tooth portion 29 of the locking protrusion 27, and “d”represents the outside diameter of the restraining gear 42.

That is, the clearance between the restraining member 4 and the supportportion 33 is set narrow to the degree that contact between therestraining gear 42 and the locking tooth portion 29 does not occur.

From the aforementioned Equation, the length of engagement between therestraining member 4 and the upper case is set long so that it meets thefollowing dimensional relationship:

a≧(b×d)/(2×c).

As a second form of the tilt suppressing structure, in the case ofproviding the urging member 5 formed from a coil spring, as shown inFIG. 6, the following dimensional relationship is set in order tosuppress the tilt of the restraining member 4 by regulating the tilt ofthe urging member 5 with respect to a spring receiver 34 formed on theinside surface of the upper case 31:

e≦(2×f×c)/d

where “c” represents the space in the unlocked state between therestraining gear 42 and the locking tooth portion 29, “d” represents theoutside diameter of the restraining gear 42, “e” represents theclearance between the outer periphery of the urging member 5 and theinner periphery of the spring receiver 34, and “f” represents the lengthof engagement between the urging member 5 and the spring receiver 34.

That is, the clearance “e” between the restraining member 4 and thesupport portion 33 is set narrow to the degree that the contact betweenthe restraining gear 42 and the locking tooth portion 29 does not occur.The urging force of the urging member 5 in the circumferential directionis equalized, so the restraining member 4 can be held parallel. Also,the engagement length “f” between the urging member 5 and the springreceiver 34 is made long so that it meets the aforementioned Equation.

As a third form of the tilt suppressing structure, the slide portion 41a of the restraining member 4 that slides on the slide portion 61 a ofthe unlocking member 6 has a curved surface, which has a radius ofcurvature (R) of 30 mm or less. It is preferable that the radius ofcurvature (R) be 20 mm or less and further preferable that it be 15 mmor less. With this, the restraining member 4 is liable to return to aflat state if the radius of curvature is smaller, when the restrainingmember 4 returns to the flat state by oscillation of the slide portion41 a caused when the circumferential urging force produced by the urgingmember 5 becomes unequal because of the tilt of the restraining member4.

As a fourth form of the tilt suppressing structure, the lower end of theleg portion 63 of the unlocking member 6 in the locked state is providedto project from the lower end (addendum circle) of the reel gear 24,because the space between the restraining gear 42 and the locking toothportion 29 becomes large and the allowable tilt angle of the restrainingmember 4 can be made large, if the quantity of movement of the unlockingmember 6 is increased when the unlocking operation is performed (seeFIG. 1). With this arrangement, when the driving gear 13 meshes with thereel gear 24, the leg portions 63 of the unlocking member 6 are pushedup before the driving gear 13 meshes with the reel gear 24. For thisreason, the extent to which the leg portions 63 are pushed up until thedriving gear 13 completely meshes with the reel gear 24, that is, theextent of movement of the unlocking member 6 becomes large. Therefore,the space between the restraining gear 42 and the locking protrusion 27becomes large in the unlocked state.

As a fifth form of the tilt suppressing structure, in order to similarlymake the space between the restraining gear 42 and the lockingprotrusion 27 larger in the unlocked state, the slide portion 41 a ofthe restraining member 4 and the slide portion 61 a of the unlockingmember 6 are provided so that they contact each other in the lockedstate shown in FIG. 1. That is, the restraining member 4 at the loweredposition (locked state) does not always need to abut the unlockingmember 6, because the restraining gear 42 meshes with the locking toothportion 29 and is stopped. However, if there is clearance between therestraining member 4 and the unlocking member 6 when the unlockingmember 6 moves in the unlocking direction, the quantity of movement ofthe restraining member 4 is reduced by the quantity of the clearancewith respect to the quantity of movement of the unlocking member 6.Therefore, if the restraining member 4 and the unlocking member 6 are incontact with each other in the locked state, the gap between therestraining gear 42 and the locking tooth portion 29 can be made largerin the unlocked state, while assuring the extent of movement of therestraining member 4.

As a sixth form of the tilt suppressing structure, in order to make thegap between the restraining gear 42 and the locking tooth portion 29larger in the unlocked state even if the extent of movement of therestraining member 4 during the unlocking operation is the same, thespace “c” between the restraining gear 42 and the locking tooth portion29 is set greater than or equal to the whole depth “t” of therestraining gear 42 (see FIG. 5). That is, the relationship between cand t is set to c≧t. It is preferable that the relationship be c≧1.2tand further preferable that it be c≧1.4t. If teeth are the same inshape, increasing the number of teeth of the restraining gear 42 canreduce the whole tooth depth “t” and make the aforementioned space “c”larger. Therefore, when the restraining member 4 tilts slightly, thecontact between the restraining gear 42 and the locking tooth portion 29can be prevented. In addition, a reduction in the pitch between adjacentteeth in the restraining gear 42 reduces slackening or stretching ofmagnetic tape in the locked state.

Note that practically, the aforementioned various tilt suppressing formsare constructed in combination so that the tilt of the restrainingmember 4 is prevented.

Furthermore, in the present invention, the reel-rotation restrainingmeans adopts a structure for preventing the disengagement of themagnetic tape from a tape leader pin which is caused by the magnetictape pulled in the locked state by falling shock, etc.

The restraining gear 42 of the restraining member 4 and the lockingtooth portion 29 have a triangular cross section, as illustrated in FIG.7. Each tooth of the locking tooth portion 29 on the side of the reel 2has a front inclined face 29 b which faces in the winding direction(indicated by an arrow W) and a rear inclined face 29 a which faces inthe reverse winding direction (indicated by an arrow U). On the otherhand, each tooth of the restraining gear 42 on the restraining member 4has a front inclined face 42 a which abuts the rear inclined face 29 aof the locking tooth portion 29 when the reel 2 is rotated in thereverse winding direction (indicated by an arrow U), and a rear inclinedface 42 b which abuts the front inclined face 29 b when the reel 2 isrotated in the winding direction (indicated by an arrow W).

In the tooth of the restraining gear 42, the apex angle γ is within 90degrees, the interior angle α of the front inclined face 42 a withrespect to a vertical plane “s” is 30 degrees or greater, the interiorangle β of the rear inclined face 42 a with respect to the verticalplane “s” is 30 degrees or greater, and α and β are approximately thesame. In the tooth of the locking tooth portion 29, as with the tooth ofthe restraining gear 42, the apex angle γ′ is within 90 degrees, theinterior angle α′ of the rear inclined face 29 a with respect to avertical plane s′ is 30 degrees or greater, the interior angle β′ of thefront inclined face 29 a with respect to the vertical plane s′ is 30degrees or greater, and α′ and β′ are approximately the same. However, γis greater than or equal to γ′. That is, the restraining gear 42 and thelocking tooth portion 29 are formed in a range of 60°≦γ′≦γ≦90° and30°≦α, β, α′, β′≦45°.

Note that the restraining gear 42 and the locking tooth portion 29 areformed in conical form so that the whole tooth depth of the outerperipheral portion becomes higher. Thus, the outer peripheral portionsmesh each other earlier.

Now, a description will be given of the operation of the reel-rotationrestraining means 10. In a non-operative state, such as an archivedstate, etc., of the magnetic tape cartridge 1 shown in FIG. 1, therestraining member 4, the unlocking member 6, and the reel 2 are movedto the side of the lower case 32 of the cartridge case 3 by the urgingforce of the urging member 5. The center opening 32 a in the lower case32 is closed by the reel 2. The unlocking member 6 is at the loweredposition where the bottom surface abuts the top surface of the bottomwall 21 a of the reel hub 21. The lower ends of the leg portions 63 ofthe unlocking member 6 project from the tooth edge of the reel gear 24.The restraining member 4 abutting the top surface of the unlockingmember 6 is also at its lowered position. The locking tooth portion 29of the reel 2 mesh with the restraining gear 42 of the restrainingmember 4. Thus, the restraining member 4 restricts rotation of the reel2 and is in a locked state of preventing the operation of loading themagnetic tape.

On the other hand, in the operative state of FIG. 2 in which themagnetic tape cartridge 1 is loaded into the drive mechanism of therecording-reproducing unit, the rotating shaft 12 of the rotation means11 approaches the bottom surface of the reel 2. Also, the driving gear13 meshes with the reel gear 24 and moves and holds the reel 2 slightlyupward. Then, the tooth edges of the driving gear 13 abut the lower endsof the leg portions 63 of the unlocking member 6 and push them up. As aresult, the unlocking member 6 moves upward against the urging force ofthe urging member 5, and the restraining member 4, along with thisunlocking member 6, also moves in the upward unlocking direction. Thisunlocks the engagement between the teeth of the restraining gear 42 andthe locking tooth portion 29, whereby the reel 2 becomes free to rotate.In this unlocked state, the magnetic tape is loaded or unloaded by thedrive mechanism of the recording-reproducing unit.

In the locked state, the tilt of the restraining member 4 is suppressedor removed by adopting the aforementioned various forms of the tiltsuppressing structure. Also, the gap between the restraining gear 42 andthe locking tooth portion 29 is made larger in the unlocked state.Therefore, the contact between the restraining gear 42 and the lockingtooth portion 29 is prevented, the occurrence of an undesirable sound isprevented, and a hindrance to rotation of the reel 2 is prevented. Inthis manner, the magnetic tape can be rotated without being subjected toa load of some magnitude.

In addition, since the interior angels α and β of the inclined faces ofeach tooth of the restraining gear 42 and the interior angles α′ and β′of each tooth of the locking tooth portion 29 is set between 30 and 45degrees, the reel 2 can be reliably locked in the meshed state betweenthe restraining gear 42 and the locking tooth portion 29. Furthermore,even if the restraining gear 42 and the locking tooth portion 29 areshifted in phase from each other when they are locked, the extent ofmovement due to the mesh between the restraining gear 42 and the lockingtooth portion 29 will be slight in the reverse winding direction and thewinding direction. The slack of the magnetic tape is also slight, so apulling force that is exerted on the magnetic tape by the movement ofthe reel 2 in the winding direction W is small. Therefore, thedisengagement of the magnetic tape from a tape leader pin due to forcedlocking can be prevented.

When, in the aforementioned locked state, the reel 2 is rotated in thewinding direction W by falling shock, etc., and an excessive pullingforce is exerted on the magnetic tape, the restraining member 4 is movedupward in the unlocking direction against the urging member 5 by theinclined faces 42 a and 29 a of the restraining gear 42 and the lockingtooth portion 29 which face in the reverse winding direction U, becausethe interior angles of the inclined surface 42 a and 29 a are 30 degreesor greater. With the upward movement of the restraining member 4, therestraining gear 42 and the locking tooth portion 29 are disengaged fromeach other and the reel 2 is rotated in the reverse winding direction U,that is, the tape slackening direction, so pulling force is reduced andalleviated. Thus, stretching and disengagement of the magnetic tape canbe prevented.

While the present invention has been described with reference to thepreferred embodiments thereof, the invention is not to be limited to thedetails given herein, but may be modified within the scope of theinvention hereinafter claimed.

What is claimed is:
 1. A magnetic tape cartridge comprising: a cartridgecase where a single reel with magnetic tape wound thereon is rotatablyhoused; and reel-rotation restraining means which, when the cartridgecase is not used, goes to a locked state to restrict rotation of saidreel and, when the cartridge case is used, goes from said locked stateto an unlocked state to allow said rotation; said reel-rotationrestraining means having a restraining member for restricting rotationof said reel by moving toward or away from said reel, an urging memberfor urging said restraining member in a restraining direction, and anunlocking member for moving said restraining member in an unlockingdirection, by rotating integrally with said reel and moving according toa chucking operation of rotation means of a drive unit; wherein saidrestraining member has a restraining gear which meshes with a lockingtooth portion formed in said reel to restrain rotation of said reel;said urging member is supported by a spring receiver formed in saidcartridge case; and the following relationship is met:  e≦(2×f×c)/dwhere “c” represents the space between a tooth of said restraining gearin said unlocked state and said locking tooth portion, “d” representsthe outside diameter of said restraining gear, “e” represents theclearance between an outer periphery of said urging member and an innerperiphery of said spring receiver, and “f” represents the length ofengagement between said urging member and said spring receiver.